It kind of looks like a landscape? Of course we live in landscapes so it is natural for us to see the horizon. It grounds us and helps us orient ourselves within our physical world.  It also creates a starting point for depicting the our physical world in the abstract. We see a horizon because we cannot see around a ball which happens to be floating in infinite space. Think about that a minute. If there were an end to the space in which our universe exists, what would be on the other side? No end, just more horizons. Can our life be the same way? I think so!